Depression is common in patients with Parkinson?s disease (PD) and is a major factor negatively impacting quality of life. To date, there have been no well-designed clinical trials of antidepressant pharmacotherapy for depression in PD. Although selective serotonin reuptake inhibitor (SSRI) antidepressants are often viewed as first-line treatment for depression, their efficacy and tolerability in PD have not been established. In particular, concerns have been raised that they might worsen Parkinsonian motor function. Proposed is a series of activities to develop the elements essential to conduct a randomized, double blind, placebo-controlled, parallel groups trial of the SSRI paroxetine for patients with PD and depression. During the one-year planning grant, collaborative arrangements will be solidified and adequate plans for subject recruitment will be made. Case report forms and a complete manual of study operations and procedures will be developed. At the end of the planning grant, everything will be in place for the clinical trial itself. The clinical trial has been designed to determine the efficacy of paroxetine in reducing depressive symptoms. Information regarding the effects of paroxetine on quality of life, motor function, cognition and its general tolerability will also be obtained. One hundred twenty subjects will be enrolled among 6 centers and each subject will participate in the trial for 12 weeks. The planning grant will set the stage for the clinical trial that will clarify many important questions regarding the optimal pharmacotherapy of depression in patients with PD.